JP2001153793A - Method and apparatus for preventing deposition to optical member of absorption spectroscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and a system for preventing adhesion to optical parts in a spectroscopic sensor. SOLUTION: The novel method provided for preventing adhesion to optical parts in an absorption spectroscopy measurement cell includes a step of carrying out an absorption spectroscopy measurement of a sample gas introduced into the cell 200, and a step of introducing a flow of a purge gas from a purge gas inlet pipe 232 on a critical surface of the optical part 210 at a velocity effective to prevent adhesion to the critical surface. A gas inlet is disposed adjacent to the critical surface. Also provided are an apparatus for executing the inventive method, the measurement cell useful in the absorption spectroscopy measurement, an apparatus for executing the absorption spectroscopy measurement and a semiconductor-processing apparatus.

Description

DETAILED DESCRIPTION OF THE INVENTION

CROSS REFERENCE TO RELATED APPLICATIONS This application is provisional application No. 60, filed July 19, 1999, the entire contents of which are incorporated herein by reference.
U.S.A./144,181. S. C. §119
(E).

[0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel method and apparatus for preventing adhesion to optical components in an absorption spectrometry cell. The invention also relates to a measuring cell useful in absorption spectroscopy measurements. The invention further relates to a device for performing absorption spectroscopy measurements and to a semiconductor processing device.

[0003]

2. Description of the Related Art Semiconductor integrated circuits (ICs) are manufactured by a series of processes, and most of the processes use gas. Such processes include etching, diffusion, chemical vapor deposition (CVD), ion implantation, sputtering, and rapid thermal processing. Methods of monitoring impurities in such processes using an in-line absorption spectroscopy cell are described, for example, in Mc Co.
No. 5,963,336 to Andrew et al.

[0004] Sensitivity in detecting gas phase molecular species by absorption spectroscopy increases as the optical path through the sample increases for a given pressure and concentration. The intensity of the light beam reaching the detector is given by Beer's Law:

[0005] _{^I = I} 0 · ^e _{-α cPl} Here, _{I o} is the incident radiation intensity, alpha is the absorption rate, l is the path length through the sample, c is the concentration (volume concentration) of the impurity in the sample, P Is the total pressure of the sample. If the absorption is small, the amount of light absorbed is given by:

[0006] It is often impractical to keep the beam and detector remote from each other in order to increase I- _Io = αcPll. Therefore, "folded" light paths are often used, in which case
A mirror reflects the light beam back and forth many times through the sample gas.

The Herriott design is often preferred for tuned diode laser absorption spectroscopy (TDLAS). As shown in FIG. 1, an exemplary Elliott cell 100 includes two cylindrical gas sample cells 104 mounted on opposite sides of a conventional cylindrical gas sample cell 104.
One curved mirror 102 is used. Other types of multi-pass cells are well known. U.S. Pat. No. 3,524,066 to Blakkan, which is incorporated herein by reference.
Simple multi-pass devices such as those described in U.S. Pat. No. 5,173,749 to Cell et al. A planar polygon multiple pass cell is described in U.S. Pat. No. 5,818,578 to Inman et al, the contents of which are incorporated herein by reference.

In-cavity laser absorption spectroscopy (W. Brunn)
er and H.E. Paul's "Theory of Selective Intracavity Absorption (On the theory of select)
live intracavityabsorbio
n) "Optical Communications 12 (3) 252 (1974)) is also known as intracavity laser spectroscopy (see US Patent No. 5,723,864 to Atkinson et al.) It is based on the principle of absorption of a laser beam in a laser cavity. Ring-Down Spectroscopy of Cavities (A. O'Keefe et al., "Cavity Ring-Down Spectrometer for Absorption Measurements Using a Pulsed Laser Source").
meter for absorption m
easements using pulsed
laser sources) ”, revised scientific measurement 59
(12) 2544 (1988) and U.S. Patent No. 5,973,864 to Lehman et al.) Are based on the absorption of a laser beam within an external cavity. Both of these methods are considered to be sophisticated types of absorption spectroscopy. These provide very high sensitivity and also rely on optics in which the probe beam passes through the cavity many times and thus has a very high reflectivity.

The various gases used in the semiconductor manufacturing process mentioned above are highly reactive and tend to adhere when they come into contact with the surface, especially under IC manufacturing conditions such as high temperatures and plasma conditions. Inline spectroscopy sensors
When used to monitor processes in such aggressive atmospheres, deposits due to process gases tend to form on sensor surfaces including, for example, optical component surfaces such as light reflecting mirrors and light transmissive windows. is there.

[0010] Deposits formed on the optical components of the spectroscopic cell can adversely affect sensitivity and operability of the sensor. For example, deposits formed on the reflective surface of a mirror attenuate its reflectivity, and thus the intensity of the light that is reflected many times and subsequently reaches the detector. Similarly, the formation of deposits on the light transmissive window through which light rays enter and exit the measurement cell will attenuate the light intensity reaching the detector. Such attenuation of light intensity reduces measurement sensitivity and may eventually lead to a state where the sensor does not function at all.

Deposits on mirrors and light transmissive windows have traditionally been removed by disassembling the sensor and mechanically / chemically cleaning contaminated components. However, such maintenance is inconvenient and uneconomical. Therefore, it is desirable to avoid or minimize deposits.

US Pat. No. 5,36 to Borden et al.
No. 0,980 discloses a practical sensor for monitoring the practical level of a processing chamber by scattering light. To prevent contamination by corrosive or coating species in the effluent generated by the process, the gas is flowed through a gas purification line at a flow rate less than that of the gas being removed from the processing chamber in the discharge line. Purifies optical components. It is not desirable to use such a large flow rate of the purification gas because a large load is applied to the vacuum pump. as a result,
It is necessary to replace the discharge line with a large-diameter one and, if possible, the vacuum pump with a large-capacity one. In addition, the possibility of back contamination of the processing chamber is increased.

[0013]

SUMMARY OF THE INVENTION To meet the requirements of the semiconductor processing industry and overcome at least some of the disadvantages of the related art, the present invention provides a novel method for preventing adhesion to optical components useful in absorption spectroscopy. It is an object to provide a method and an apparatus. This can avoid or significantly improve the problems associated with the formation of deposits on optical components such as mirrors and light transmissive windows in the absorption spectroscopy cell. In particular, the present invention can minimize the flow of the purge gas with a flow rate less than the flow rate of the gas being exhausted from the processing chamber. Thereby, the required flow rate of the purified gas can be minimized.

It is a further object of the present invention to provide an in-line cell useful in absorption spectroscopy and to provide an apparatus for performing absorption spectroscopy measurements with a novel device for preventing adhesion.

It is a further object of the present invention to provide a semiconductor processing device having an in-line cell according to the present invention.

[0016] Other objects and aspects of the present invention will become apparent to those skilled in the art from a reading of this specification, the accompanying drawings and the claims.

[0017]

According to a first aspect of the present invention, deposition on optical components in an absorption spectroscopy measurement cell, such as a tunable diode laser, an intracavity or cavity ringdown spectroscopy cell, is provided. A new method of prevention is provided. The method according to the present invention performs absorption spectroscopy measurements on the sample gas introduced into the cell and purifies the critical surface of the optic at a rate effective to prevent deposition on the critical surface. Introducing a flow of purified gas from a gas intake pipe. The gas inlet is located adjacent to the critical surface.

In accordance with a further aspect of the present invention, there is provided an apparatus useful in an absorption spectroscopy cell for preventing adhesion to optical components. The apparatus according to the present invention comprises a purge gas intake pipe for introducing a flow of purge gas at a rate effective to prevent adhesion on the critical surface of the optical component to the critical surface. The gas inlet is located adjacent to the critical surface.

According to a further aspect of the present invention, there is provided a measuring cell useful for absorption spectroscopy measurements. This measuring cell is
In addition to the adhesion preventing device as described above, a sample gas inlet, a sample gas outlet, a sample area, a light inlet port, and a light outlet port that is a dual-purpose or another port are provided. . Each of these ports is in optical communication with the sample area and has a light transmissive window.

According to a further aspect of the invention, there is provided an apparatus for performing absorption spectroscopy measurements. The apparatus comprises a measurement cell as described above, a light source for generating light rays passing through the cell from a light entrance port, and a detector for measuring light rays exiting the cell from a light exit port.

According to a further aspect of the present invention, there is provided a semiconductor processing apparatus. The apparatus includes a semiconductor processing apparatus including a substrate processing chamber, a discharge line connected thereto, and a device for performing the above-described absorption spectroscopy.

The present invention relates to, for example, methane in a sample,
It is particularly applicable to in situ absorption spectroscopy, which is useful for measuring, for example, accurately and sensitively the concentration of gas phase molecular impurities such as humidity (water vapor) and carbon dioxide. According to the present invention, the surface of an optical component such as a mirror or a light-transmitting window can be maintained in a state of no deposits.

In the case of a mirror used in absorption spectroscopy, the invention ensures that the surface of the mirror is not attenuated by deposits formed thereon.
Similarly, if the surface of the optical component belongs to a light transmissive window, the present invention ensures that the light transmissive properties of that window do not degrade.

The present invention is directed to a system in which normal gas flow is directed onto critical surfaces of the optics and normal gas flow is minimized by properly designed gas inlets and control of gas velocity. It is particularly adaptable to prevent adhesion to optics used for in situ measurement of gas composition.

[0025]

DETAILED DESCRIPTION OF THE INVENTION FIGS. 2A and 2B show cross-sectional views of an exemplary in-line cell 200 useful for absorption spectroscopy according to one aspect of the present invention. Although this exemplary cell is an Elliott-type multi-pass cell, the concepts of the present invention described below are not so limited, and other cells with optical components, such as, for example, intra-cavity cells and cavity ring-down cells. It will be clear that it is easily adaptable to the cell of the configuration.

This in-line cell 200 includes a sample area 202. Preferably, the walls of the cell define a substantially cylindrical space through which the sample gas flow passes. Sample gas flows from the sample intake port 204 through the cell into the sample region 202 and exits the cell at the withdrawal port 206.

This intake port 204 is to be connected to a source of the sample to be measured. As described above, the advantages of the present invention can be realized if the intake port 204 can be connected to the discharge line of a semiconductor processing tool that enables in-situ measurement. In this way, the concentration of the molecular gas species in the processing tool exhaust gas can be measured. The outlet port 206 is typically connected to a foreline of a vacuum pump or other evacuation means, such as a fan or blower. The inlet and outlet ports can be connected to the sample source and outlet means, respectively, using well-known means such as flanges and flexible hoses.

The cell includes one or more mirrors 210 that reflect light rays through the sample area. In this exemplary embodiment, a plurality of preferred curved mirrors 210 are located along the interior of the cell. Note that the structure of this mirror changes depending on whether it functions as part of the entrance or exit structure of the light beam. The mirrors each have a light reflective surface facing the sample area, and light rays incident on the cell pass through the sample area until each mirror reflects the light at least once before exiting the cell. Are arranged to be reflected from one mirror to another.

Preferably, the light reflecting surface is a polished metal. Since it is desirable that these surfaces have a high reflectivity, they can be coated with one or more layers of reflective materials, such as gold or other metal layers or high reflectivity dielectric coatings, to reflect their reflectivity. Rate can be increased.

The cell further includes a light input / output port 212 that allows light rays to enter and exit the cell. As shown, the mirror 210 includes a through-passing aperture 214 that forms part of an incoming / outgoing port through which light rays can pass. In this exemplary embodiment,
There is one port through which light rays enter and exit the cell,
A structure having a plurality of ports is also conceivable. Thus, light rays can enter and / or exit the cell from the same or separate ports that are open to the cell, and can enter and / or exit the cell from multiple incoming or outgoing ports. Further, the ports can be located on the same side of the cell or on separate sides.

The light input / output port 212 includes a light transmissive window 216 that allows light rays to enter and exit the cell through the sample area. In the exemplary embodiment, the light transmissive window 216 is in the aperture 214 of the mirror. Light transmissive materials suitable for this window are well known and include, for example, aluminum oxide, quartz, magnesium fluoride, and the like.

In addition to the above, the light-transmitting window 216 may have a coating layer on a surface opposite to the surface facing the sample area to reflect a part of the light beam. Subtracting the signal due to the reflected portion from the transmitted portion of the light beam will provide a more accurate absorbance measurement otherwise. Among the commercially available coating materials, metallic coatings are preferred.

As shown in this exemplary embodiment, the light transmissive window 216 is preferably offset by a certain angle from perpendicular to the incident light. While Brewster's angle is effective and preferred as the bias angle, angles less than the Brewster's angle are generally more convenient and effective. By biasing the window in this way, coherent interference caused by reflective portions of the light beam can be avoided. As a result, more accurate measurement is possible. Such biasing is further served for a similar purpose as the optional coating layer described above. That is, a more accurate measurement value can be obtained by subtracting the signal due to the background noise using the reflection part of the light beam.

The cell 200 should be substantially hermetically sealed so that gas samples can be measured at less than atmospheric pressure, ie, in a vacuum. As a result, in-situ measurements in vacuum processing tools such as those used in the semiconductor manufacturing industry can be effectively performed. To ensure that the measurement cell remains airtight, the mirror 210 can be sealed using an O-ring or other type of vacuum seal known to those skilled in the art.

One or more purge gas streams are introduced into the cell through purge gas inlets 230 and 232 to prevent deposits from accumulating on one or more optical components.
In this exemplary embodiment, gas inlet 230 is associated with a mirror having light transmissive window 216, while gas inlet 232 is associated with a mirror at the opposite end of the cell. Oxygen, hydrogen, other reactive gases, a combination of reactive gases or a combination of an inert gas and a reactive gas may be used, but the purifying gas may be nitrogen,
Preferably, it is an inert gas selected from the group consisting of argon, helium and combinations thereof. For example, when SiO ₂ is deposited from gas phase SiO, the SiO is reduced to SiH ₄ and H ₂ O by hydrogen purification, thereby preventing the formation of SiO ₂ deposits.

The location, size and upstream pressure of the purge gas inlet are such that this purge gas is completely blown away by the purge gas stream where the critical surfaces of the optics are essentially not mixed with the main exhaust gas stream. It is designed to be directed at the critical surface of the optic at speed. The term critical surface, as used in this document, comes into contact with light from a light source,
It also refers to the part of the optical component for which it is desirable to prevent adhesion. Purified gas flow control is achieved, for example, using a mass flow controller, an orifice having a constant upstream pressure, and / or other flow control devices.

Although a constant flow of the purification gas may be used, the purification gas may be pulsed and flown. The use of a pulsed stream can further minimize the use of purge gas for a given stream. The flow is pulsed using well-known flow control techniques such as placing a ballast vessel and a solenoid valve after the upstream pressure regulator so that the solenoid valve is opened and closed for a desired time using a controller. Can be

In the case of a continuous flow or a pulsed flow,
It is desirable to deliver the purge gas at a rate sufficient to blow off the entire critical surface while minimizing the total flow of purge gas. Although the flow rate of the purification gas varies depending on the shape of the apparatus and the pressure and flow rate of the sample gas, the flow rate of the gas is generally about 5 to 100 sccm, but when the total flow rate flowing through the cell exceeds about 10 slm. Is about 10 sl
m.

FIG. 3A shows a more detailed cross-sectional view of an exemplary apparatus 300 for preventing adhesion to optical components included in the cells of FIGS. 2A and 2B. Apparatus 300 includes a mirror stage 302, a mirror 210, and a flow directing device 306. These parts are shown in more detail in FIGS. 4 (A) and (B), FIGS. 5 (A) and (B), and FIGS. 6 (A) and (B), respectively.

Purification gas is introduced into the apparatus 300 from a gas pipe (not shown). The flow paths in the device are indicated by arrows.
As can be seen, the gas flows through the bore 30 of the mirror stage 302.
8 and a plurality of gas injection orifices 31 of stage 302
0 through the front surface of the mirror 210. The gas flow is in a direction substantially parallel to the front surface of the mirror. If the gas pressure in the sample cell 200 is less than about 1 Torr,
The gas pressure upstream of the orifice is typically about 1-20
Thor. The gas pressure upstream of the orifice is
Desirably, it is at least twice the pressure during 00. The diameter of the gas injection orifice 310 is preferably about 50 to 100 μm, and more preferably about 500 μm or less. The distance between adjacent orifices is preferably no greater than about 3 mm along the periphery of the stem portion 320 of the mirror step 302. The orifice 310 is preferably about 0.5-5 mm above the front surface of the mirror, but is typically about 1 mm on the front surface of the mirror.

FIG. 3B shows a light entrance port aperture 212 having a mirror stage and a light transmitting window 21.
3A, except that a mirror aperture 216 holding an aperture 6 is included.

FIGS. 4A and 4B show the mirror stage 30.
2 is a sectional view and a plan view, respectively. As shown in FIG. 4B, the plurality of gas injection orifices 310 are used.
Is preferably distributed symmetrically around the central axis of the mirror stage such that the purged purge gas is blown off over the critical surface of the optical component.

FIGS. 5A and 5B are a cross-sectional view and a plan view, respectively, of an exemplary mirror 210 used in the adhesion preventing device. The mirror 210 has an aperture 5 along the central axis.
01, which allows the mirror to be placed on the mirror stage by inserting the stem portion 320 of the mirror stage from the aperture 501. The aperture 214 also has the light transmissive window 21
6 exists. In the illustrated embodiment using one window to allow light to enter and exit the cell, the mirrors on the other side of the cell are identical to each other but have no window or aperture.

FIGS. 6A and 6B are a cross-sectional view and a plan view, respectively, of the purifying gas flow directing device 306.
The shape of the flow directing device should be selected to provide sufficient flow over the surface of the optic to prevent accumulation of unwanted deposits on its critical surfaces.
In this exemplary embodiment, the flow directing device is circular in shape, which captures and completes the circular mirror with each other.

The purge gas directing device includes an aperture 602 that fits over the stem portion 320 of the mirror stage 302 for mounting the flow directing device 306 to the mirror stage 302. The flange portion 604 is a surface for controlling and directing the flow of the purification gas over the entire surface of the optical component. This flow directing device 306
Is preferably located just above the gas injection orifice 310, more preferably about 2 mm above the front surface of the mirror 210, and most preferably about 10 mm above the front surface of the mirror.

The arrangement of the injection orifice 310, the mirror 210, and the gas flow directing device 306 provide sufficient gas velocity to blow away the critical surfaces of the mirror. Quite surprisingly, in order to purify effectively, the velocity of the purge gas molecules in a direction parallel to the mirror surface need not exceed the typical molecular velocity in the exhaust gas. For example, if the exhaust line is at 25 ° C., the average velocity of molecules such as nitrogen in the exhaust gas is about 500 m / s (average over all directions).

FIG. 7 shows the results of a computer simulation of the purified gas flowing over the entire surface of the mirror. This simulation was obtained under typical operating conditions, including a total flow of 20 sccm on one mirror. The simulation shows that the velocity contour at 1 cm from the purified gas supply is about 1 cm.
m / s.

It is believed that this result can be explained by simply assuming that the cleaned area corresponds to a cylinder with a height of 3 mm at the mirror surface. In this case, if the flow rate on the mirror surface is 20 sccm, the overall molecular flow rate at 1 cm radius is about 1.7 × 1
0 ^-3 atm m / s. The simulation results show that the local density at the mirror surface is equal to about 1 Torr. Under these conditions, the molecular mean free path is about 1 μm. Thus, molecules in the exhaust gas that enter the purge gas stream are subjected to about 3000 collisions. Thus, while the velocity of the purge gas molecules in the purification direction is much lower than the velocity of the colliding molecules, the number of collisions with the purge gas that the colliding molecules must undergo can be maintained by keeping the mirror surface normal. Believed to be sufficient.

The mirror cleaning apparatus described herein has been found to be effective in protecting the optical system from accumulation of deposits and chemical erosion by gas phase reactive species in the exhaust line. If particles are also present, additional measures are desirable. A sufficiently large particle traveling at a sufficient velocity may enter the purge gas stream while another molecule of the same velocity does not. If deposition of particles is a problem, it may be desirable to position the optics perpendicular to the exhaust gas flow and / or to retract the optics slightly back from it. If the optics is at right angles to the gas flow, it is common to retract it about 21 cm behind, but it is sufficient to position it behind about 1 cm or more.

In the exemplary embodiment shown in FIG. 2, the downstream mirror is perpendicular to the gas flow, while the upstream mirror is not. In such a case, in order to minimize adhesion to the upstream mirror surface, the downstream mirror should be placed further behind the cell outlet, for example, about 12 cm from the cell outlet.
You may make it recede behind by more than cm. If this retraction dimension is minimized, the particles will not penetrate into the purge gas stream.

There are advantages to using a purge gas inlet with a circular mirror. When a circular mirror is generally used in an Elliott cell as shown, its critical surface is close to the circumferential surface, so its center is not optically significant. Thus, the purging gas inlet is located at the central portion of the mirror, whereby purifying gas can be supplied from the center of the mirror to the periphery to the outside.

In a further refinement, the purge gas can be directed to cover the most important parts of the periphery, if not the entire periphery. For example, in an Elliott-type cell, light strikes a mirror in a circular multiple spot pattern. The purge gas introduction system can be configured such that one or more orifices correspond to each spot and direct the purge gas over the spot portion. Other designs are also possible. For example, square, rectangular or other shaped mirrors can be used in the present invention.

In addition, purifying gas schemes other than those described above may be used. For example, when the center of the cell is a cell used in an intracavity type or cavity ring-down type spectroscopic cell, for example, a purification gas flows from the outer peripheral portion of the optical component toward the central axis thereof. It is also possible. In such a case, it is desirable to keep the center of the mirror free of deposits.

As a result of the present invention, the shape of the purifying gas injector is
It is shaped so that the gas can be directed onto the critical surface. As a result, the flow rate of the purge gas is minimized, which is particularly desirable in the case of vacuum processing equipment, since it does not adversely affect the pumping requirements. The localization of the gas flow near the critical surface minimizes the flow of purified gas. As a result, the need for retrofitting vacuum systems with large capacity pumps is eliminated.

According to a further aspect of the present invention, the optical component can be heated. This is advantageous in certain circumstances in helping to prevent adhesion to optical components. The optimum temperature will vary from process to process, but generally the optical surface will be at about 50-150 ° C, preferably about
Can be heated to ~ 100 ° C. This heating may be direct heating or indirect heating. General optical surface heating structures and methods are described in McAn, the entire contents of which are incorporated herein by reference.
US Patent No. 5,949,537 to Drew et al. and In
No. 6,084,668 to Man et al.

In the case of indirect heating, the mirror stage can be heated, which in turn heats the optical surface. Suitable heaters include, but are not limited to, resistance heaters, self-regulating heaters such as heat traces, heating lamps, induction heaters, and optional recirculating liquid or gas phase heating fluids. is there. One example of such a structure is shown in FIGS. 3A and 3B, in which a resistive cartridge heater 3 embedded in a mirror stage 302 is shown.
22 is shown. An electrical lead 324 is connected to one end of the heating component of the cartridge heater 322 and the other end is connected to a power source.

In addition or instead of the above, the purifying gas may be heated. Preferably, such heated gas is localized to the surface of the window or the reflective surface of the mirror, effectively preventing adhesion of the optic to critical surfaces.
The purge gas may be heated prior to introduction into the cell using, for example, a resistive heater or other heat exchange techniques known to those skilled in the art.

Although the exemplary in-line cell is an Elliott design, the inventive concept is readily adaptable to other types of in-line cells. For example, this inventive concept is applicable to any form of cell that complies with the above conditions with respect to polygonal multi-pass or optics and cleaning structures.

The in-line cell should be made of a material compatible with the atmosphere contained therein. Such materials are within the knowledge of one skilled in the art. For example, various forms of stainless steel can be used for the cell surface in contact with the sample to be measured.

Although this inventive cell can be used for any absorption spectroscopy technique, laser spectroscopy,
Especially tuned diode laser absorption spectroscopy (TD
LAS). Referring to FIG. 8, such an apparatus 800 is directed from a light transmissive window 804 into the sample area of the cell, in addition to the in-line cell described above with reference to FIGS. 2A and 2B. A light source 800, preferably a diode laser, for generating a light beam. To measure the light rays exiting the cell from this light transmissive window, the device further comprises a main detector 8
06, which may be, for example, a photodiode.

As long as a suitable light source is available, any molecular impurities of interest can be detected.
For example, steam, nitric oxide, carbon monoxide, hydrogen fluoride,
Silicon tetrafluoride and other fluorides and methane and other hydrocarbons can be detected by measuring the decay of light from a diode laser light source that emits light that characterizes the impurities.

Measurement sensitivity is improved by a laser light source that emits light in the spectral region where the target molecule absorbs the strongest. In particular, light sources that emit wavelengths longer than about 2 μm are preferred because many of the molecular impurities of interest have strong absorption bands in this region.

Any suitable wavelength tunable light source may be used. Among the currently available light sources, diode laser light sources are preferred because of their narrow line width (less than about 10 ⁻³ cm ⁻¹ ) and relatively high intensity at the emission wavelength (approximately 0. 1 to several milliwatts)
Because.

Examples of diode lasers include Pb salt type and GaAs type diode lasers. Pb
Operating a salt type laser to emit infrared light (having a wavelength of more than 3 μm) requires cryogenic temperatures, while a GaAs type diode laser operates at near room temperature and operates in the near infrared (0. 8 to 2 μm).

Recently, GaAs (or other I such as AsP)
Diode lasers containing Sb in addition to II-V compound pairs have been described (“Mid-infrared wave gas sensing”).
length enhancetrace gas se
nsing) ", R.S. Martinelli, Laser Focus World, 19
(See March, 1996, p. 77). These diodes emit light at wavelengths above 2 μm when operating at -87.8 ° C. Such a low temperature is not convenient, but the low temperature required by a Pb salt type laser (−170
(Less than ° C).

An example in which a similar laser having a wavelength of 4 μm operates at 12 ° C. has also been reported (see “Laser and Optics (Las
ers and Optronics) ", March 1996
Month issue). Most preferably, a diode laser of the type described above operates at a temperature of at least -40C.
With thermoelectric coolers that control temperature at such temperatures, these light sources are less complex than low temperature diode systems.

To make these lasers more advantageous, it is important to improve their optical properties from current levels. For example, a single-mode diode (ie, one in which emission at a fixed temperature and drive current occurs at a single wavelength and emission at other wavelengths with at least 40 dB less intensity) should be available. is there.

The suitable light source used in the present invention is not limited to the above-mentioned diode laser. For example, other types of lasers of similar size and tunable by simple electrical means are also contemplated, such as fiber lasers and quantum cascade lasers. Commercial use of such a laser is also conceivable.

The apparatus further includes a light source 8
At least one mirror 808 or lens that reflects 10 from the light transmissive window into the cell and at least one additional mirror 81 that reflects light exiting the cell to the main detector
2 may be included. Optionally, mirror 80
A lens may be used instead of 8 and 814.

Since the light from the diode laser light source diverges, the mirror 808 is preferably curved to collimate the light beams. Similarly, mirror 814 is preferably curved to focus this parallel light beam on the main detector.

A second detector 816, which may also be a photodiode, measuring a portion of the light beam 818 reflected from the light transmissive window 804, and means for subtracting this reference signal from the measurement obtained by the main detector; May be optionally provided in the present apparatus. Literature (eg, Mo
ore, J .; H. "Building Scientific Equipment (Buil
Ding Scientific Apparatus
s) ", Addison Wesley, London, 19
If there is an operational amplification zone in a configuration such as that described in 1983, it can operate as a means for subtracting this reference signal.

The reflected light does not absorb any light due to the molecules in the sample area, and thus serves as a reference signal.
Light source variations are compensated for by subtracting the reference signal from measurements of light passing through the cell (measured by the main detector). This also improves sensitivity to signal variations due to molecules in the system chamber 820.

Although "double ray" techniques by subtracting the reference signal are well known, these techniques usually require a subtle beam splitter, ie, optics whose sole function is to split the rays. And According to the present invention, the entrance window to the chamber can provide this function without requiring any additional components. The ratio of transmitted light to reflected light at this window can be controlled by appropriate coating on the window.

This inventive device is particularly suitable for detecting and / or measuring the concentration of molecular species in a gas exhausted from a vacuum chamber. In such a case, the cell can be located in the evacuation line between the vacuum chamber and the vacuum pump system.

This device is compatible with a wide range of materials. For example, the vacuum chamber can contain certain reactive or non-reactive (inert) gas species, which can be in a plasma state or a non-plasma state. Examples of reactive gases that are compatible with this inventive device include H ₂ , O _{2, as} well as SiH ₄ , HCl, and Cl ₂ if the humidity level is less than 1000 ppm.
Any inert gas such as N ₂ , Ar, Ne or He can be used in the inventive device. When the inventive device is used in a plasma environment, the device is preferably mounted at least about 6 inches from the plasma zone to minimize the formation of deposits on windows and other cell surfaces.

Since the above detection device can be used in a plasma environment or a non-plasma environment together with an inert gas or a reactive gas, the present device can be used in a semiconductor processing apparatus.
Particularly suitable for use in monitoring gas phase molecular species such as water vapor. By using the detection device together with the semiconductor processing device, gas-phase molecular impurities can be monitored on site in real time.

The apparatus can easily be adapted to virtually any semiconductor processing apparatus using a vacuum system. Examples of such an apparatus include an etching apparatus, a diffusion apparatus, a chemical vapor deposition (CVD) apparatus, an ion implantation apparatus, a sputtering apparatus, and a rapid thermal processing apparatus.

FIG. 9 shows a semiconductor processing apparatus 900 having an in-line cell 200 and an apparatus 800 for performing absorption spectroscopy as described in detail above. The apparatus further has a vacuum chamber 902 in which a semiconductor substrate 904 is placed on a substrate holder 906. One or more gas inlets 908 are provided to deliver one or more gases to the vacuum chamber.

The vacuum chamber is evacuated from the discharge opening 910 of the vacuum chamber. Part or all of the volume of the total displacement from the processing tool can be introduced into the cell 911. Vacuum pump 9 for evacuating the vacuum chamber
12 is connected to the device either directly or via a vacuum line. The pump discharge line 914 can be connected to a pump 912, which can be connected to another pump or a gas scrubber (not shown). Examples of vacuum pumps that can be used include mechanical rotary or booster pumps, diffusion pumps, cryogenic pumps, absorption pumps, and turbomolecular pumps.

Further, while the case where the vacuum pump and measuring device are located below the vacuum chamber is shown, those skilled in the art will readily appreciate that other orientations are also possible.

Although the present invention has been described in detail with reference to specific embodiments thereof, various changes and modifications can be made without departing from the scope of the appended claims, and equivalents can be used. It will be clear to those skilled in the art.

[Brief description of the drawings]

FIG. 1 is a diagram of a conventional absorption spectroscopy cell designed by Elliott.

2A and 2B are a top plan view and a side cross-sectional view, respectively, of an exemplary in-line cell according to a further aspect of the present invention.

FIGS. 3A and 3B are cross-sectional views of an exemplary device with and without light transmissive windows, respectively, to prevent adhesion on optical components, according to one embodiment of the present invention. It is.

4A and 4B are a sectional view and a plan view, respectively, of a mirror stage of the device shown in FIG. 3;

5A and 5B are a sectional view and a plan view, respectively, of the mirror of the device shown in FIG. 3;

FIGS. 6A and 6B are a cross-sectional view and a plan view, respectively, of the purified gas flow discharge device shown in FIG. 2;

FIG. 7 is a result of a computer simulation for flowing a cleaning gas over a mirror surface.

FIG. 8 is a top view of a light source / detector scheme in an apparatus for performing absorption spectroscopy measurements according to a further aspect of the present invention.

FIG. 9 is a side sectional view of a semiconductor processing apparatus according to a further aspect of the present invention.

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Benjamin Julsic 78470 Saint-Remy-le-Chevreuse, France, Rue des Mercières 21 (72) Inventor Carroll Schnepper Clarendon, 60514, Illinois, United States, United States Hills, Indian Drive Earl 23 (72) Inventor Ronald Inman United States, 60534, Illinois, United States 60534, Lions, West Forty-Fifth Place 8714 (72) Inventor Dmitry Zunamensky United States, 60559, Illinois, Darien No. 221, Lakeview Drive 1526 (72) Inventor Tracy Jackseal 60532, Illinois, United States Tarongu Court 6199

Claims (34)

[Claims] 1. A method for preventing adhesion to an optical component in an absorption spectroscopy cell, performing absorption spectroscopy measurement on a sample gas introduced into the cell, and traversing an important surface of the optical component. And introducing a flow of the purge gas at a rate effective to prevent deposition on said critical surface from a purge gas intake pipe positioned adjacent to the critical surface. 2. The method of claim 1, wherein the flow of the purge gas introduced across the critical surface is pulsed. 3. The optical device according to claim 1, wherein the optical component is a mirror.
The method described in. 4. The method of claim 3, wherein said cell is an Elliott-type cell. 5. The method of claim 1, wherein the purge gas flows across the critical surface in a direction from a central axis of the optical component toward an outer periphery of the optical component. 6. The method of claim 5, wherein the purge gas intake pipe comprises a plurality of purge gas injection orifices through which the purge gas flows. 7. The plurality of purge gas injection orifices,
7. The method of claim 6, wherein the method is disposed on the critical surface and injects the purge gas in a direction substantially parallel to the critical surface. 8. The gas inlet of claim 1, wherein the gas inlet has a circular cross-sectional shape, and the plurality of purge gas injection orifices are substantially equally spaced along a periphery of the gas injector. 7. The method according to 7. 9. The method of claim 1, wherein the purge gas intake pipe includes a plurality of purge gas injection orifices through which the purge gas flows. 10. The method according to claim 1, wherein the purifying gas is about 5 to 100 scc.
The method according to claim 1, wherein the method is introduced from a purge gas intake pipe at a flow rate of m. 11. The method of claim 1, wherein said purge gas is an inert gas selected from the group consisting of nitrogen, argon, neon, helium, and combinations thereof. 12. The method of claim 1, wherein the purge gas is a reactive gas or a combination of a reactive gas and an inert gas. 13. The method according to claim 12, wherein said reactive gas is oxygen or hydrogen. 14. The method of claim 11, wherein the critical surface of the optical component is approximately 50
The method of claim 1, further comprising heating to a temperature of １５０150 ° C. 15. The sample gas is introduced into the cell through a sample gas inlet and removed from the cell through a sample gas outlet, thereby establishing a flow path for the sample gas in the cell. The method of claim 1, wherein the critical surface of the optical component is recessed from the flow path. 16. The method of claim 1, wherein said sample gas is introduced into said cell from a semiconductor processing chamber via a sample gas inlet. 17. An apparatus for preventing adhesion to an optical component useful in an absorption spectroscopy cell, wherein the flow of a purification gas is prevented from crossing the important surface of the optical component. A purging gas inlet pipe for introducing at a rate effective for said gas inlet, said gas inlet being located adjacent said critical surface. 18. The apparatus of claim 17, further comprising means for pulsing the flow of the purge gas introduced across the critical surface. 19. The gas intake pipe is disposed along a central axis of an optical component, such that the purification gas traverses the critical surface in a direction from the central axis to an outer periphery of the optical component. 18. The apparatus of claim 17, wherein the flow is as follows. 20. The apparatus of claim 19, wherein the purge gas intake pipe includes a plurality of purge gas injection orifices through which the purge gas flows. 21. The method of claim 20, wherein the plurality of purge gas injection orifices are located above the critical surface and eject the purge gas in a direction substantially parallel to the critical surface. Equipment. 22. The gas inlet has a circular cross-sectional shape, and the plurality of purge gas injection orifices include:
22. The device of claim 21, wherein the device is substantially evenly distributed along a periphery of the gas injector. 23. The apparatus of claim 22, further comprising a flow directing device for directing a flow of the purge gas from the gas inlet onto the critical surface. 24. The apparatus of claim 23, wherein said flow directing device is located above said critical surface and said gas injection orifice. 25. The apparatus according to claim 24, wherein said optical component is a mirror. 26. The apparatus of claim 17, wherein the purge gas intake pipe includes a plurality of purge gas injection orifices through which the purge gas flows. 27. The apparatus of claim 17, further comprising a heater for heating said critical surface of said optical component. 28. The apparatus according to claim 28, further comprising a step for placing the optical component, wherein the heater is connected to the step.
28. The device according to claim 27. 29. The apparatus according to claim 27, wherein said optical component is a mirror. 30. A system comprising a sample gas inlet, a sample gas outlet, and a sample area, wherein the light input port and the light output port are the same or separate ports, and each of said ports is 18. A measurement cell useful in absorption spectroscopy, comprising optically communicating with a sample area, including a light-transmissive window, and comprising the device for preventing adhesion to optical components according to claim 17. 31. The method according to claim 31, wherein the inlet and the outlet are
31. The measurement cell according to claim 30, wherein a flow path for the sample gas to pass through the cell is set, and the important surface of the optical component is recessed from the flow path. 32. The measuring cell according to claim 30, wherein:
An apparatus for performing absorption spectroscopy, comprising: a light source for generating a light beam incident on the cell from the light input port; and a detector for measuring the light beam exiting the cell from the light output port. 33. The apparatus according to claim 32, wherein the absorption spectrometer is a tunable diode laser absorption spectrometer, an in-cavity spectrometer, or a cavity ring-down spectrometer. 34. A semiconductor processing apparatus comprising: a semiconductor processing apparatus including a substrate processing chamber and a discharge line connected to the substrate processing chamber; and the apparatus for measuring absorption spectroscopy according to claim 30.